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DEVELOPMENT  OF  PLANT  COMMUNITIES  OF  A 
SAND  RIDGE  REGION  IN  MICHIGAN 


(WITH  TWELVE  FIGURES) 


W.  G.  WATERMAN 


V 


/- 

Reprinted  for  private  circulation  from 
The  Botanical  Gazette,  Vol.  LXXIV,  No.  i,  September  1922 


'VV 


VOLUME  LXXIV 


NUMBER  1 


THE 

BOTANICAL  GAZETTE 

Septe7fiber  IQ22 

DEVELOPMENT  OF  PLANT  COMMUNITIES  OF  A 
SAND  RIDGE  REGION  IN  MICHIGAN 

W.  G.  Waterman 

(with  twelve  figures) 

Plant  synecology  is  the  study  of  the  relations  of  plant  communi- 
ties to  their  environment.  The  subject  may  be  divided  into  three 
major  sections. 

1.  Morphological  and  physiological  synecology. — The  physiog- 

nomy, ecological  structure,  and  floristic  composition  of  plant  com- 
munities and  their  relationship  to  the  factors  of  the  environment. 
This  includes  not  merely  an  enumeration  of  the  species  and 
ecological  forms  present,  but  also  the  sociological  value  of  the  dif- 
ferent members  of  the  community,  as  suggested  in  the  following 
topics:  abundance,  dominance,  affiliation,  genetic  importance, 

constancy,  etc. 

2.  Geographic  synecology. — The  distribution  of  plant  communi- 
ties, with  special  reference  to  the  influence  of  the  factors  of  environ- 
ment. 

3.  Genetic  or  dynamic  synecology. — The  study  of  the  develop- 
ment of  plant  communities  on  unit  areas  as  the  result  of  the  action 
of  biotic  factors,  modified  by  physiographic  influences  and  by 
changes  of  cHmate. 

In  the  early  days  of  ecology,  the  distributional  phase  of  synecol- 
ogy was  more  evident  and  was  followed  with  almost  no  suggestion 

I 


725752 


2 


BOTANICAL  GAZETTE 


[SEPTEMBER 


of  the  others.  In  recent  years  the  other  phases  have  been  increas- 
ingly studied,  but  all  have  generally  been  combined  in  a more  or 
less  haphazard  fashion.  In  a geographically  extended  treatment  of 
the  subject,  the  distributional  (geographic)  division  may  either 
precede  or  follow  the  developmental  (genetic)  division.  If  the 
communities  are  considered  merely  from  the  standpoint  of  their 
floristic  content,  their  distribution  may  be  studied  first,  and  this 
has  been  the  historical  order.  Plant  geography  has  been  studied 
with  increasing  interest  since  the  days  of  von  Humboldt,  and  it 
is  still  an  important  branch  of  synecology.  It  is  evident,  however, 
that  the  distribution  of  communities  identified  and  named  in 
accordance  with  their  position  in  a developmental  series  (associ- 
ations, formations,  etc.)  cannot  be  carried  out  adequately  until  a 
genetical  study  of  those  communities  has  been  completed.  In  a 
limited  area  the  study  of  the  distribution  of  communities  is  cor- 
respondingly hmited,  and  is  of  value  only  as  it  helps  to  determine 
the  developmental  relationships  of  these  communities. 

As  genetic  synecology  is  the  most  recent  branch  of  the  subject, 
and  its  content  is  not  yet  fully  organized,  a brief  historical  statement 
will  be  in  order  at  this  point.  Cowles  (3)  was  the  first  to  form  a 
comprehensive  system  based  on  the  dynamic  element  in  plant  com- 
munities, as  a result  of  his  difficulty  in  classifying  the  communities  of 
the  Chicago  region  in  accordance  with  Warming’s  principles.  He 
was  so  strongly  impressed  with  the  influence  of  the  physiographic 
factors  that  he  outlined  his  system  on  that  basis.  Later  (4)  he 
recognized  climatic,  physiographic,  and  biotic  factors  as  the  three 
great  causes  of  plant  succession. 

Clements  (i)  pointed  out  that  climatic  and  physiographic 
causes  produce  succession  but  not  true  development,  that  is,  the 
building  up  of  a quasi-organism;  and  that  this  was  possible  only 
by  the  action  of  biotic  factors,  and  especially  by  the  influence  of 
the  plants  which  compose  the  different  communities.  Clements 
bases  his  main  divisions  on  his  climaxes  or  ‘‘formations,”  his  next 
division  is  into  primary  and  secondary  successions,  and  his  third 
into  hydrosere  and  xerosere,  based  on  the  water  content  of  the  initial 
area.  For  these  divisions  he  also  uses  as  adjective  modifiers  the 
term  hydrarch  and  xerarch,  suggested  by  Cooper  (2).  As  these 


WA  TERM  A N—PLA  NT  COMMUNITIES 


3 


1922] 

latter  refer  especially  to  the  beginning  of  the  succession,  they  are 
more  suitable  in  this  connection  than  such  terms  as  hydrosere,  etc., 
which  apply  to  the  moisture  content  of  the  whole  succession,  because 
in  most  cases  the  initial  moisture  condition  does  not  persist,  and  the 
substratum  generally  approaches  a mesophytic  condition.  While 
this  classification  may  be  logically  defensible,  Clements  does  not 
give  sufficient  consideration  to  the  fact  that  the  actual  lines  of 
development  are  determined  by  the  nature  of  the  substratum,  that 
the  floristic  content  of  the  pioneer  stages  is  absolutely  different  in 
clay,  sand,  or  rock,  and  that  it  is  only  as  the  seres  approach  the 
climax  stage  that  they  begin  to  converge  and  to  resemble  each  other. 
Furthermore,  standing  water  should  be  regarded  as  a type  of  sub- 
stratum, because  its  pioneer  stages  are  practically  identical  in  ponds 
on  rock,  sand,  or  clay,  and  are  quite  different  from  the  pioneer 
stages  of  wet  sand  or  clay,  to  which  stages  the  term  hydrarch 
should  be  restricted.  The  subdivisions  of  the  primary  succession 
(prisere),  therefore,  should  be  sand  succession  (psammosere) , clay 
succession  (geosere),  rock  succession  (lithosere),  and  aquatic  suc- 
cession (hydrosere).  The  first  three  successions  have  wet  and  dry 
initial  stages  (hydrarch,  xerarch).  It  is  evident  that  this  classifi- 
cation does  not  distinguish  the  many  types  of  substratum  containing 
mixed  sand,  clay,  and  gravel.  It  does  not  seem,  however,  that  these 
are  sufficiently  well  marked  or  sufficiently  different  as  to  vegetation 
to  warrant  establishing  one  or  more  additional  seres  for  them  at 
present. 

The  terminology  of  the  units  of  genetic  synecology  is  being  much 
discussed  at  present.  It  is  generally  agreed  that  the  fundamental 
unit  in  the  developmental  classification  of  communities  is  the  associ- 
ation. At  first  this  was  defined  in  terms  of  the  habitat,  but  in  1921 
Nichols  (7),  as  a result  of  several  questionnaires  sent  to  eighty-five 
ecologists,  reported  at  the  recent  meeting  of  the  Ecological  Society 
of  America  at  Toronto  that  a large  majority  of  the  ecologists  con- 
sulted favored  the  following  statements:  (i)  That  the  term  plant 
association  be  recognized  as  apphcable  both  to  the  abstract  vegeta- 
tion concept  and  to  the  concrete  individual  pieces  of  vegetation 
upon  which  this  concept  is  based;  (2)  that  plant  association  in  the 
abstract  be  defined  somewhat  as  follows:  an  ecological  vegetation- 


4 


BOTANICAL  GAZETTE 


[SEPTEMBER 


unit  characterized  by  an  essentially  definite  physiognomy  and 
ecological  structure,  and  by  an  essentially  definite  floristic  composi- 
tion as  regards  dominant  species;  (3)  that  plant  association  in  the 
concrete  be  defined  somewhat  as  follows:  a plant  community  of 
essentially  uniform  (or  homogeneous)  physiognomy  and  ecological 
structure  and  of  essentially  uniform  (or  homogeneous)  floristic 
composition  as  regards  dominant  species.  This  simply  formulates 
the  more  or  less  unconscious  practice  of  most  ecologists,  who,  when 
speaking  of  ‘‘a  Scirpus-Typha  association”  have  a concrete  com- 
munity in  mind,  while  “the  Scirpus-Typha  association”  of  a certain 
region  is  plainly  an  abstract  concept. 

The  next  higher  unit  is  also  generally  recognized  as  the  forma- 
tion, but  there  is  not  yet  the  same  agreement  in  regard  to  its  content 
as  there  seems  to  be  for  the  association.  The  following  brief  survey 
of  the  progress  of  opinion  in  regard  to  the  formation  is  summarized 
from  Tansley  (9).  According  to  the  definition  adopted  by  the 
Brussels  Congress,  the  formation  is  composed  of  associations  which 
differ  in  their  floristic  composition,  but  are  in  agreement  (i)  with 
the  conditions  of  the  habitat,  and  (2)  as  regards  their  growth  forms. 
Tansley  says,  “ Though  this  concept  is  apparently  accepted  by  most 
European  phytogeographers,  it  has  little  real  hold  on  actual  concrete 
research  because  it  is  abstract  and  one  sided.”  In  1907  Moss  (5) 
proposed  a unit,  later  embodied  by  Tansley  (8),  in  which  all 
associations  developed  on  the  same  habitat  or  on  one  of  essentially 
constant  character  were  considered  as  belonging  to  one  formation. 
Not  all  the  stages  of  a succession  were  necessarily  included  in  one 
formation.  If  the  habitat  obviously  changed  its  character  com- 
pletely, it  was  recognized  that  a new  formation  had  been  initiated. 
This  conception  was  widely  criticized,  and  Tansley  admitted  the 
vahdity  of  criticisms  of  the  habitat  element  in  the  definition. 
Clements  (i)  refused  to  recognize  any  formations  except  those  de- 
termined by  climate,  regarding  all  communities  in  a region  where 
forests  are  climatically  possible  only  as  stages  in  the  development 
of  forest  formations.  Tansley  believes  that  this  view  has  not  been 
generally  accepted  in  Europe  or  in  America,  and  feels  that  the  uni- 
versal dominance  of  cHmatic  factors  as  determinants  of  climax 
vegetation  has  not  been  proved. 


1922] 


WA  TERM  A N—PLA  NT  COMMUNITIES 


5 


Nichols  (6)  recognized  this  and  returned  to  Schimper’s  dis- 
tinction between  climatic  and  edaphic  formations.  His  unit  next 
above  the  association  was  the  edaphic,  later  called  the  physiographic 
formation,  which  he  defined  as  the  association-complex  occupying  a 
physiographic  unit  area,  while  the  climatic  formation  was  a complex 
of  physiographic  formations  forming  the  vegetation,  taken  in  its 
entirety,  of  any  region  in  which  the  essential  climatic  relations  are 
similar  or  uniform  throughout.  This  Tansley  criticized,  because 
“nothing  hke  a sharp  line  can  be  drawn  between  one  climatic  region 
and  another,  so  that  it  becomes  impossible  to  delimit  climatic  forma- 
tions in  Nichols’  sense.”  Tansley  accepts  Clements’  “associes” 
for  all  stages  which  have  not  reached  a relatively  stable  (climax) 
condition,  and  defines  the  association  as  a mature  quasi-organism 
which  is  relatively  fixed  and  stable.  He  then  defines  the  formation 
as  including  “all  the  vegetation  which  is  naturally  grouped  around 
the  association,  determined  by  the  particular  collection  of  environ- 
mental factors  which  make  up  the  ecological  conception  of  the 
habitat.”  Nichols  has  not  published  as  yet  any  further  statement 
on  the  formation,  but  in  his  paper  at  the  Toronto  meeting  he  seems 
to  adhere  to  his  division  of  formations  as  physiographic  and  climatic. 

As  a result  of  a study  of  literature  on  formations,  as  well  as 
actual  conditions  in  the  field,  especially  in  connection  with  the 
preparation  of  the  present  paper,  the  writer  has  reached  the  follow- 
ing conclusions,  on  which  the  definitions  of  the  terms  involved  will 
be  based. 

1 . That  there  is  a distinct  advantage  in  omitting  from  the  defini- 
tion of  the  formation  all  reference  to  the  habitat,  as  was  done  in  the 
case  of  the  association. 

2.  That  it  is  inadvisable  to  connect  the  idea  of  the  formation 
with  a climax  association,  because  the  determination  of  climax  is 
one  of  the  purposes  of  a genetical  study,  and  it  is  clearly  undesirable 
to  define  a term  which  should  be  usable  from  the  beginning  of  a study 
in  such  a way  that  it  cannot  properly  be  used  until  the  study  has 
been  completed.  In  such  a case  it  would  be  necessary  to  secure  an 
additional  term  for  the  community  in  the  process  of  development. 
This  is  cumbersome  and  unsatisfactory,  as  is  illustrated  in 
Clements’  use  of  “associes”  and  “association,”  which  does  not 


6 


BOTANICAL  GAZETTE 


[SEPTEMBER 


seem  to  meet  with  general  approval  in  this  country  at  least.  In 
this  case  there  is  the  additional  objection  that  the  more  familiar 
and  convenient  term  is  restricted  in  use  to  a minority  of  cases. 

3.  That  the  double  aspect,  abstract  and  concrete,  approved  for 
the  association  be  recognized  also  for  the  formation.  The  abstract 
concept  of  the  formation,  indicated  by  the  use  of  the  definite  article, 
would  thus  correspond  with  the  Brussels  Congress  description,  and 
would  constitute  the  formation  abstract  as  a sort  of  ecological 
species.  The  formation  concrete  might  then  be  regarded  simply 
as  any  association  complex,  characterized  by  a dominant  association 
but  including  all  adjacent  associations,  whether  mature  or  imma- 
ture, and  other  more  or  less  anomalous  or  unidentified  communities 
connected  with  them.  Thus  the  formation  concrete  in  general 
would  correspond  to  Nichols’  physiographic  formation,  although 
the  habitat  is  omitted  from  the  definition,  and  contiguity  made 
the  basis  on  which  the  communities  are  united  in  the  formation. 
Individual  formations  may  be  named  either  from  the  dominant 
association  or  from  the  physiographic  nature  of  the  area  occupied. 

4.  If  a unit  above  the  formation  is  desired,  it  will  be  found  con- 
venient to  associate  the  formations  of  a region  in  a larger  group, 
which  Nichols  (6),  following  Schimper,  has  characterized  as  a 
climatic  formation.  Tansley  has  demonstrated  the  inadvisability 
of  the  term,  but  the  fact  remains  that  the  concept  is  a convenient 
one,  especially  for  field  use,  and  the  writer  suggests  that  the  term 
“formation  complex,”  or  simply  “complex,”  be  used  for  this  con- 
cept. If  it  be  objected  that  complex  is  equally  applicable  to  lower 
grades  of  units,  and  is  actually  in  use  with  them,  a special  term, 
such  as  “aggregate,”  might  be  employed.  It  does  not  seem  advis- 
able to  use  the  term  formation,  even  if  qualified  by  a descriptive 
adjective,  for  two  classes  of  units  of  different  grade.  Indeed  this 
concept  may  be  identified  sufficiently  by  general  expressions  already 
in  use,  such  as  vegetation,  formations,  or  even  forest  (as  in  “vege- 
tation of  Connecticut,”  “formations  of  the  Great  Lakes  region,” 
“temperate  deciduous  forest,”  etc.). 

On  the  whole,  it  seems  advisable  to  follow  Tansley  and  Nichols 
in  emphasizing  the  vegetational  content  of  the  community  and 
regarding  the  habitat  as  the  sum  total  of  the  environmental  factors. 


922] 


WA  TERM  A N— PLANT  COMM  UNITIES 


7 


and  therefore  not  employing  it  to  indicate  any  definite  portion  of 
the  surface  of  the  earth.  There  is  an  advantage  in  employing  a 
special  term  for  the  ground  occupied  by  each  synecological  unit, 
and  the  writer  tentatively  uses  the  word  “locality”  for  the  ground 
occupied  by  an  individual  association,  “area”  ^ for  that  occupied  by 
a formation,  and  “region”  for  that  occupied  by  a formation  complex. 

The  present  study  is  to  be  regarded  as  a preliminary  reconnois- 
sance  rather  than  as  a completed  work.  Its  purpose  is  to  indicate 
the  lines  along  which  such  a study  should  proceed,  and  to  suggest 
some  tentative  conclusions.  It  is  the  intention  of  the  writer  to 
make  a thorough  study  of  the  morphology  and  physiology  of  these 
communities,  and  in  the  light  of  those  results  to  review  the  tentative 
conclusions  now  reached.  This  preliminary  survey  will  also  serve 
to  introduce  the  region  to  ecologists,  and  to  show  the  unusual  oppor- 
tunity for  the  study  of  the  very  diverse  communities  of  a region 
in  relatively  primitive  condition.  Incidentally  the  writer  regards 
the  region  as  one  which  should  be  included  in  a list  of  regions  to  be 
preserved  in  their  natural  condition. 

Description  of  habitat 

Geography. — The  region  is  located  in  Benzie  County,  Michigan, 
and  adjoins  on  the  north  the  Crystal  Lake  Bar  region  already 
reported  (lo) . It  may  be  described  as  a right-angled  triangle  whose 
base  is  about  eight  miles  long,  extending  south-southeast  from  a 
point  on  the  shore  of  Lake  Michigan  about  two  miles  northeast  of 
Point  Betsie,  almost  to  the  town  of  Honor  on  Platte  River.  The 
east  side  of  the  region  is  the  perpendicular  of  the  triangle,  and 
extends  north  from  Honor  nearly  to  the  town  of  Empire  on  Lake 
Michigan.  The  shore  forms  the  hypothenuse,  curving  sHghtly  to 
the  south  with  a projection  at  the  mouth  of  Platte  River.  It  has  a 
total  area  of  about  twenty-five  square  miles,  of  which  perhaps  one- 
fifth  is  occupied  by  lakes  and  ponds.  The  region  is  locally  known 
as  the  Platte  Plains,  although  it  is  composed  of  sand  ridges  and  hills, 
and  the  general  reUef  is  distinctly  roUing  rather  than  flat  (fig.  i). 

The  Lake  Michigan  shore  is  bordered  by  a strip  of  moving  dunes 
ranging  from  200  to  500  yards  wide.  As  the  prevailing  winds  are 

* This  is  an  ecological  use  of  the  term,  and  differs  materially  from  its  floristic  use. 


8 


BOTANICAL  GAZETTE 


[SEPTEMBER 


from  the  southwest,  this  dune  strip  has  been  protected  by  the 
morainic  ridge  (fig.  2)  north  of  Point  Betsie,  and  the  dunes  are 
relatively  low  and  do  not  have  the  scenic  features  to  be  found  in 
similar  areas  elsewhere.  South  of  the  narrow  belt  of  moving  dunes 
are  found  the  sand  ridges,  roughly  parallel  with  the  shore,  with  inter- 
vening depressions,  some  still  containing  small  ponds.  These  ponds 
occur  almost  exclusively  in  the  portion  of  the  region  west  of  Platte 


River,  probably  because  of  the  protection  of  the  morainic  ridge 
which  has  prevented  them  from  being  filled  by  blown  sand.  Be- 
tween the  sand  ridges  lies  a wide  trough  of  relatively  shght  depth, 
which  contains  a series  of  six  lakes,  more  or  less  completely  con- 
nected and  draining  into  the  Platte  River,  and  three  small  lakes 
draining  to  the  north  through  Otter  Creek. 

Geology. — This  region  is  regarded  as  having  been  a shallow 
embayment  of  Lake  Algonquin,  whose  shores  were  formed  by 


WATERMAN— PLANT  COMMUNITIES 


9 


1922] 


morainic  uplands.  The  shore  line  of  the  embayment  is  clearly 
traceable  along  the  southern  and  eastern  border  of  the  Platte  Plains 
as  shown  on  the  map.  On  the  west  the  old  shore  line,  protected  by 
the  morainic  ridge,  is  marked  by  low  rounded  knolls,  but  on  the 
south  and  east  it  still  shows  the  characteristics  of  a wave-formed 
bluff  (fig.  3).  This  feature  has  been  continued  by  wave  action  in 
the  lakes  on  the  south,  and  it  is  especially  marked  on  the  east,  where 
it  borders  the  floodplain  of  Otter  Creek  (fig.  7) . There  it  still  remains 
as  a steep  bank  rising  150  or  200  feet  above  the  plains.  The  present 


Fig.  2. — View  toward  southwest  over  shore  dunes  to  morainic  ridge  which  formed 
the  Algonquin  shore  on  the  south. 

sand  ridges  with  intervening  depressions  were  formed  originally  as 
sand  bars  by  the  receding  waters  of  Lake  Algonquin,  assisted  by  the 
winds,  which  piled  dunes  of  varying  heights  up  to  100  feet  above 
Lake  Michigan  on  the  successive  beaches  left  bare  by  the  receding 
lake.  One  morainic  fragment  is  found  on  the  present  shore  line  half 
a mile  east  of  the  mouth  of  Platte  River,  in  shape  like  a hogback, 
with  a very  steep  forested  slope  on  the  south  and  an  equally  steep 
bluff  of  erosion  facing  the  lake  (fig.  10).  The  line  of  hills  between 
Platte  Lake  and  Little  Platte  is  a morainic  remnant  exactly  in  fine 
with  the  fragment  on  the  shore.  Morainic  gravel  has  been  found 


lO 


BOTANICAL  GAZETTE 


[SEPTEMBER 


in  at  least  one  spot  midway  between  the  two ; so  it  seems  probable 
that  these  represent  the  remains  of  a moraine  which  originally 
bisected  the  triangle,  and  which  later  determined  the  location  of 
Platte  River. 

Environmental  conditions. — ^The  factors  of  the  environment 
are  similar  to  those  of  the  Crystal  Lake  Bar  region  (lo),  and  will  not 
be  repeated  here.  A study  of  the  soil  acidity  by  Wherry’s  method 
is  planned  for  the  near  future,  and  will  probably  yield  interesting 
results.  The  variations  in  soil  and  moisture  content  are  evidently 


Fig.  3. — View  toward  the  southwest  over  Platte  Lakes,  showing  Algonquin  shore 
line  in  distance. 


of  great  importance.  The  substratum  consists  in  the  main  of 
beach  and  dune  sand,  but  there  is  a mixture  of  morainic  material 
around  the  edges  where  moraine  clay  and  gravel  were  washed  down 
by  the  waves  of  Lake  Algonquin  and  by  atmospheric  agencies  since 
that  time.  The  materials  of  the  low  morainic  ridge  which  bisect 
the  area  are  also  of  considerable  importance,  and  their  significance 
will  be  considered  in  connection  with  the  migration  of  the  deciduous 
forest  elements  into  the  sand  ridge  vegetation. 

While  the  slight  moisture  content  of  the  superficial  layer  of 
sandy  soil  is  generally  recognized,  it  has  been  thought  that  the 


1922] 


WATERMAN— PLANT  COMMUNITIES 


II 


moister  conditions  of  lower  layers  and  the  low  wilting  coefficient  of 
sand  would  prevent  a serious  deficiency  of  moisture  for  plants 
adapted  to  that  habitat.  The  very  dry  weather  in  the  first  part  of 
the  summer  of  1921,  however,  apparently  caused  serious  results,  al- 
though the  full  effects  of  these  conditions  cannot  yet  be  determined. 
The  leaves  of  the  blueberries  and  other  small  shrubs  dried  up  early, 
and  while  the  plants  were  not  killed,  their  vegetative  development 
for  the  following  summer  was  greatly  reduced.  A number  of  oak 
and  pine  seedlings  up  to  two  feet  in  height  were  evidently  killed. 


Fig.  4. — Typical  sand  ridge  vegetation,  with  Pteris  aquilina  in  center 


Similar  ‘‘red  summers”  were  reported  by  the  farmers  as  having 
occurred  at  intervals  of  eight  or  ten  years.  It  is  evident  that  they 
would  profoundly  affect  the  development  of  a dense  growth  of  trees 
on  these  ridges.  Various  fires,  chiefly  prehistoric,  have  also  had 
an  influence.  The  areas  which  were  affected  by  these  fires  should 
be  determined  and  mapped,  and  their  influence  on  the  present 
vegetation  more  definitely  determined. 

Morphology  and  distribution  of  communities 

Moving  dune  formation. — The  dune  vegetation  is  practically 
the  same  as  that  of  the  Point  Betsie  dune  complex  already  described 


12 


BOTANICAL  GAZETTE 


[SEPTEMBER 


(lo,  ii),  with  the  important  exception  that  there  are  numerous 
groves  of  Pinus  Banksiana  occupying  depressions  just  back  of  the 
foredune,  and  apparently  originating  in  pannes. 

Sand  ridge  formation. — The  sand  ridge  area  was  originally 
covered  by  a forest  of  pine  and  oak  whose  trees  had  reached  con- 
siderable size.  This  forest  had  been  burned  before  the  white  set- 
tlers came  to  the  region.  Many  of  the  dead  trees  were  cut  while 
still  standing,  and  many  of  their  stumps  still  remain.  A few  patches 
were  not  burned,  perhaps  being  protected  by  neighboring  bodies 
of  water,  and  these  give  some  idea  of  what  the  original  forest 
might  have  been  (fig.  8).  Reproduction  has  been  good  all  over  the 
region,  and  with  fifty  years  ’ growth  behind  it,  the  forest  might  be 
regarded  as  half-way  to  maturity.  While  strictly  this  region  should 
be  regarded  as  a secondary  succession,  most  of  the  area  has  prac- 
tically been  untouched  by  man,  and  the  development  seems  to  be 
well  on  its  way  toward  a reproduction  of  its  original  condition,  so 
that  with  the  aid  of  apparently  untouched  portions  it  should  be  pos- 
sible to  work  out  the  stages  of  the  original  succession. 

The  trees  of  this  formation  in  the  order  of  their  importance  are 
Pinus  Strohus,  P.  resinosa,  P.  Banksiana,  Quercus  ellipsoidalis, 
Q.  alba,  Q.  rubra  (Q.  velutina  apparently  should  belong  here,  but  has 
not  been  certainly  identified),  Acer  rubrum,  Betula  alba  papyrifera, 
Populus  tremuloides,  P.  grandidentata,  Amelanchier  canadensis,  and 
Prunus  pennsyhanica.  The  shrubs  found  on  the  sand  ridges  are 
Cornus  stolonifera  near  the  dune  belt  and  Rhus  typhina  farther  south 
(fig.  4).  In  the  undergrowth  are  found  Pteris  aquilina,  GauUheria 
procumbens,  Vaccinium  mcillans,  V.  pennsylvanicum,  Melampyrum 
americanum,  and  Ceanothus  virginiana,  with  Cladonia  rangiferina, 
several  cushion  mosses,  and  occasionally  Selaginella  rupestris  in  the 
drier  portions.  In  the  more  mesophytic  spots  occur  also  Pedicu- 
laris  canadensis,  Galium  sp.,  Maianthemum  canadense,  Diervilla 
Diervilla,  and  Aster  cordifolius.  Near  the  dunes  are  found  Artemi- 
sia canadensis,  Smilacina  stellata,  Arctostaphylos  uva-ursi,  Apocynum 
cannabinum,  Rosa  blanda,  Juniperus  communis,  and  J.  horizontalis. 

Associations  of  sand  ridge  depressions. — The  depressions 
between  sand  ridges  are  small  oval  bowls  or  pockets  averaging  only 
a few  hundred  yards  in  greatest  length.  They  show  all  types  of 


1922] 


WATERMAN— PLANT  COMMUNITIES 


13 


aquatic  communities,  from  those  which  are  nearly  all  floating 
aquatics  to  the  grass  meadow  or  the  swamp  shrub  thicket.  There 
are  few  characterized  by  a true  bog  mat,  but  many  contain  charac- 
teristic bog  plants  and  shrubs.  The  grass  meadows  vary  in  size 
from  a few  yards  in  diameter  to  one  100  yards  wide,  and  one-half 
to  three-quarters  of  a mile  long;  while  two  others  of  equal  length 
are  200-300  yards  wide  (fig.  ii).  These  are  usually  bordered  by  a 
narrow  shrub  zone  between  the  sand  ridge  and  the  meadow,  includ- 
ing Alnus  incana,  Pyrus  arbutifolia,  Rosa  Carolina,  and  Cornus  stol- 


Fig.  5. — Chamaedaphne  meadow  with  Picea  Mariana  and  Larix  laricina 


onifera.  With  the  grasses  and  sedges  in  the  smaller  meadows  are 
found  also  Hypericum  virginicum  and  Spiraea  salicifolia,  while 
occasional  specimens  of  aquatics  occur,  as  Iris  and  Sagittaria.  In 
one  case  a remarkable  growth  of  Lobelia  cardinalis  covered  one  acre 
of  meadow  with  its  scarlet  flowers. 

The  bogs  are  generally  found  at  or  near  the  border  of  a lake  or 
river,  and  are  of  two  general  types,  one  an  ericad  heath,  the  other 
a tamarack  thicket.  The.  heath  type  has  a more  or  less  continuous 
cover  of  sphagnum  with  its  usual  accompaniments:  Sarracenia 
purpurea,  Vaccinium  macrocar pon,  Drosera  rotundifolia,  Menyanthes 


14 


BOTANICAL  GAZETTE 


[SEPTEMBER 


trifoliata,  Aspidium  Thelypteris,  and  in  the  wetter  portions  Typha 
latifolia,  1 ris  versicolor,  and  Phragmites  communis  (fig.  5 ) . The  shrubs 
are  Chamaedaphne  calyculata,  Andromeda  glaucophylla,  Vaccinium 
corymbosum,  Betula  pumila,  and  rarely  Ledum  groenlandicum. 
The  trees  if  any  are  scattered,  and  include  Larix  laricina,  Picea 
mariana,  and  where  the  substratum  is  very  dry  Pinus  resinosa  and 
P.  Strohus. 

The  bogs  of  the  thicket  type  are  covered  with  a dense  growth  of 
Larix  with  some  Thuja  occidentalis , mingled  with  shrubs  of  Alnus 


Fig.  6. — Long  Lake,  with  pines  on  sandy  point;  Algonquin  shore  line  in  distance 

incana,  Betula  pumila,  Rosa  Carolina,  Chamaedaphne  calyculata, 
Andromeda  glaucophylla,  Cornus  stolonifera,  Eupatorium  perfoliatum, 
Myrica  Gale,  and  occasional  specimens  of  Cypripedium  sp.  These 
thickets  are  usually  surrounded  by  a zone  of  Thuja,  sometimes 
narrow  but  occasionally  of  sufficient  area  and  maturity  of  trees  to 
be  called  a “cedar  swamp.”  Here  are  found  in  addition  Fraxinus 
americana,  Betula  alba,  Abies  balsamea,  and  Acer  rubrum.  Around 
the  outer  edges  next  the  sand  ridge,  small  specimens  of  Tsuga 
canadensis  are  locally  found. 

In  the  cedar  forests  the  shade  is  very  heavy.  The  roots  of  the 
trees  interlace  above  the  water  or  semiliquid  muck,  while  the  under- 


1922] 


WATERMAN— PLANT  COMMUNITIES 


15 


growth  grows  on  the  peaty  soil  which  has  collected  in  hummocks 
or  on  the  layer  of  tree  roots.  Shade-tolerant  mosses  are  abundant, 
and  occasional  restricted  patches  of  sphagnum  occur.  Among 
flowering  plants  the  most  common  are  Coptis  trifolia,  Cornus  cana- 
densis, Trientalis  americana,  Maianthemum  canadense,  Aralia  nudi- 
caulis,Gaultheria  procumbens,  Viola  spp.,  and  occasionally 
borealis.  Aspidium  spinulosum  and  Osmunda  regalis  are  frequently 
found,  and  some  Taxus  canadensis. 


Fig.  7. — Algonquin  shore,  kept  steep  by  erosion  of  Otter  Creek 


Vegetation  oe  river  and  lake  borders. — In  the  Platte  Plains 
there  are  no  true  alluvial  floodplains,  and  the  shores  of  streams  and 
bodies  of  water  are  either  rather  steep  sandy  slopes,  or  else  shallow 
bays  or  lagoons  inhabited  by  one  of  the  types  of  communities  already 
described  (figs.  6,  12).  The  lakes  are  frequently  shallow  some  dis- 
tance from  shore,  and  these  shallows  generally  contain  extensive 
colonies  of  Scirpus.  There  is  usually  a fringe  of  aquatic  plants, 
including  Typha  latifolia,  Sparganium,  Sagittaria,  Scirpus,  etc.,  or  of 
shrubs  including  Myrica  Gale  and  Decodon  verticillatus.  On  flowing 
streams  the  latter  does  not  seem  to  advance  from  year  to  year, 
probably  on  account  of  being  torn  away  by  ice  in  the  spring.  In 


i6 


BOTANICAL  GAZETTE 


[SEPTEMBER 


this  region  Decodon  is  chiefly  confined  to  streams,  as  it  has  been 
observed  on  lakes  or  ponds  in  only  one  or  two  instances. 

Vegetation  of  morainic  uplands. — The  morainic  uplands 
were  covered  with  a typical  climax  beech-maple- hemlock  forest, 
which  has  been  sufficiently  described  elsewhere  (lo,  12).  In  some 
places  this  is  almost  untouched,  and  in  at  least  two  places,  near 
Lake  Michigan  on  the  west  and  south  of  Long  and  Rush  Lakes, 
the  tension  zone  between  it  and  the  sand  ridge  vegetation  is  in  prac- 
tically its  original  condition.  In  the  first  locality  this  zone  is  about 
a quarter  of  a mile  wide,  and  its  elements  mingle  with  those  of  the 
sand  ridge  formation.  On  the  south  it  descends  the  steep  Algon- 
quin terrace  to  the  shores  of  Long  Lake,  and  merges  with  the  cedar 
forest  between  Long  and  Rush  Lakes,  and  south  and  east  of  Platte 
and  Little  Platte  Lakes  (fig.  7).  North  of  Little  Platte  it  originally 
stopped  on  the  crest  of  the  steep  bluff  which  borders  the  Otter 
Creek  valley,  and  the  bluff  was  occupied  by  a xero  phytic  conifer 
association,  of  which  only  a few  patches  now  remain. 

Development  of  communities 

As  already  stated,  the  purpose  of  genetic  synecology  is  to  indi- 
cate the  successional  relationships  of  the  communities  of  a region, 
and  the  place  of  each  in  a developmental  series.  In  the  present 
study  there  is  no  rock  substratum  present,  and  only  a very  restricted 
amount  of  clay  or  gravel,  so  that  the  communities  found  are  largely 
confined  to  the  psammosere  and  the  hydrosere.  Secondary  suc- 
cessions are  present,  both  in  burned  areas  and  to  a limited  degree 
in  clearings,  but  in  the  present  paper  the  chief  concern  will  be  to 
trace  the  stages  of  the  original  succession  (prisere).  With  one  or 
two  minor  exceptions  the  influence  of  climatic  and  physiographic 
factors  is  so  slight  as  to  be  negligible,  and  the  region  is  so  young 
geologically  that  there  seems  to  be  no  necessity  for  the  consideration 
of  paleoecological  relationships. 

Sand  succession  (psammosere) 

Pioneer  stages. — Xerarch. — The  pioneer  stages  of  this  succes- 
sion are  confined  to  the  strip  of  shifting  sand  along  the  lake.  The 
initial  vegetation  includes  Ammophila  arenaria  as  the  absolute 


1922] 


WA  TERM  A N—PLA  NT  COMMUNITIES 


17 


•pioneer,  associated  with  Artemisia  caudata,  Calamovilfa  longifolia, 
Cirsium  Pitcheri,  Campanula  rotundifolia,  Cakile  maritima,  Lathyrus 
maritima,  Prunus  pumila,  Salix  longifolia,  S.  syrticola,  Senecio  vul- 
garis, Solidago  spp.,  Aster  sp.,  Zygadenus  chlorantha,  Hudsonia 
tomentosa,  Arctostaphylos  uva-ursi,  Juniperus  communis,  and  J.  hori- 
zontalis.  All  of  these  are  able  to  germinate  on  dune  sand,  but 
only  Ammophila  is  able  to  become  established  in  pure  sand.  The 
others  are  stunted  and  soon  die,  unless  their  roots  come  in  contact 
with  buried  plant  material,  from  which  apparently  they  are  able 
to  obtain  the  necessary  mineral  elements.  Ammophila  and  perhaps 
Calamovilfa  are  the  only  plants  which  cover  the  ground  thickly 
enough  to  act  as  stabilizers.  The  other  herbaceous  plants  are  also 
scattered,  and  never  grow  close  enough  to  form  a ground  cover  in 
the  moving  dune  belt.  Arctostaphylos  and  Juniperus  horizontalis 
germinate  occasionally  on  the  open  sand,  but  it  is  doubtful  whether 
they  can  stabilize.  Whenever  they  occur  in  sufficient  quantity  to 
cover  the  ground,  it  is  usually  by  invasion  from  a patch  already 
established. 

f Hy  dr  arch. — J uncus  halticus  and  willows  are  the  usual  pioneers 

in  pannes.  Occasionally  a local  patch  of  Pinus  Banksiana,  with 
more  or  less  Thuja  occidentalis , Abies  balsamea,  and  Betula  alba,  forms 
a clump  or  grove,  which  may  reach  the  size  of  several  acres  and 
spread  over  small  valleys  or  local  patches  of  level  sand.  There  is 
no  evidence  of  any  extensive  permanent  stabilization  by  coniferous 
trees  in  the  belt  of  moving  sand  next  to  the  lake.  They  frequently 
occur  as  narrow  strips  or  tongues  between  advancing  lee  slopes. 
The  transition  from  this  area  to  the  pine-oak  ridges  is  very  marked  as 
one  crosses  the  irregular  line  of  crescent-shaped  lee  slopes  and  comes 
to  the  lower  rounded  ridges,  where  the  force  of  the  wind  is  much  less 
marked  and  the  plants  of  the  pine-oak  stage  have  become  estab- 
lished. From  this  it  would  appear  that  the  coniferous  tree  stage 
originates  in  pannes,  but  does  not  really  become  widespread  so  as 
to  form  a forest  into  which  the  more  mesophytic  pines  and  oaks 
gradually  migrate  and  become  dominant,  but  that  the  coniferous 
patches  are  relatively  scattered,  and  their  only  influence  is  as 
humus  formers  and  as  centers  of  distribution  for  certain  elements 
of  the  pine-oak  stage.  Stabilization,  therefore,  is  due  to  a diminu- 


i8 


BOTANICAL  GAZETTE 


[SEPTEMBER 


tion  of  the  force  of  the  wind,  either  on  account  of  the  increasing  dis- 
tance from  the  shore  as  the  lake  waters  recede,  or  by  the  building 
up  by  the  wind  of  high  dunes  which  form  a windbreak  and  protect 
the  sand  ridges. 

Pine-oak  stage.— With  the  relative  cessation  of  sand  move- 
ment, coupled  with  increase  of  humus,  the  pine-bak  stages  begin. 
As  might  be  expected,  the  content  of  vegetation  on  the  ridges  shows 
a certain  amount  of  progressive  change,  both  in  floristic  content 
and  in  the  density  of  growth  and  mesophytism,  as  we  traverse  the 


Fig.  8. — Grove  of  old  pine,  oak,  and  hemlock,  probably  protected  by  proximity 
to  Platte  River. 


region  from  the  vicinity  of  the  lake  toward  the  south  (that  is,  from 
younger  to  older  ridges).  On  the  first  ridges  there  is  a preponder- 
ance of  conifers  and  many  relics  of  the  herbaceous  pioneers,  especi- 
ally Artemisia,  Smilacina  stellata,  Arctostaphylos,  and  Juniper  us 
spp.  The  first  tree  of  this  stage  to  come  into  the  coniferous  asso- 
ciation of  the  open  dunes  is  Pinus  Strobus,  followed  shortly  by 
P.  resinosa.  Quercus  ellipsoidalis,  Q,  alba,  and  possibly  Q.  velutina 
follow  rather  slowly,  and  now  may  be  found  fairly  evenly  distributed 
in  the  more  advanced  portions  of  the  area.  Acer  rubrum  is  very 
frequently  met  near  Platte  River,  or  in  other  somewhat  moist 


1922] 


WATERMAN— PLANT  COMMUNITIES 


19 


localities.  Betula  alba,  Populus  grandidentata,  and  P.  tremuloides 
are  fairly  common  all  through  the  region.  As  has  been  stated,  the 
region  has  been  burned  probably  more  than  once,  although  for- 
tunately not  in  recent  years.  The  extent  of  area  covered  by  any 
one  burning  is  uncertain.  Certain  local  differences  in  distribution 
can  best  be  explained  on  the  assumption  that  the  burnings  have 
not  been  very  complete;  certainly  some  patches  which  bear  old  pines 
and  hemlocks  must  have  escaped  (fig.  8),  but  patches  of  white 
birch  and  poplars  indicate  a secondary  succession  after  fires. 


Fig.  9. — Luxuriant  growth  of  Pteris  aquilina  in  mesophytic  habitat,  second 
growth  birch  and  poplar  in  background. 


The  undergrowth  varies  from  the  modified  pioneer  type  of  the 
ridges  nearest  the  lake  to  a mesophytic  type  containing  many  forms 
belonging  to  the  climax  beech-maple-hemlock  forest.  These  meso- 
phytic associations  are  not  distributed  in  accordance  with  the  geo- 
logic age  of  the  ridges,  but  are  determined  rather  by  edaphic 
conditions.  They  will  be  considered  in  the  section  on  the  beech- 
maple-hemlock  invasion.  In  addition  to  the  typical  mixed 
ground  cover  already  described,  there  are  two  types  of  undergrowth 
societies  unevenly  distributed  over  the  ridges,  an  almost  pure 
Pteris  aquilina  society  and  a Vaccinium  society  including  V.  penn- 


20 


BOTANICAL  GAZETTE 


[SEPTEMBER 


sylvanicum,  V.  vacillans,  with  considerable  Gaylussacia  haccata. 
On  the  whole,  the  Pteris  communities  are  more  characteristic  of 
the  portion  of  the  ridge  area  west  of  the  Platte  River  and  the 
Vaccinium  of  that  east  of  the  river.  No  definite  factors  determining 
the  distribution  of  these  communities  have  yet  been  established. 
The  Pteris  seems  to  be  more  moisture-requiring  than  the  Vaccinium, 
and  it  certainly  grows  more  luxuriantly  in  the  moister  habitats 
(fig.  9).  The  Vaccinium  species  are  usually  regarded  as  more  acid- 
tolerant,  and  investigations  along  these  lines  may  yield  definite 
results. 

Beech-maple-hemlock  stage. — It  is  generally  recognized 
throughout  Michigan  that  the  deciduous  hardwood  forest  is  con- 
fined to  rich  clay  or  loamy  soil,  white  pine  forests  are  found  on 
sandy  loam,  and  the  pioneer  conifers  on  poor  sandy  soil.  The 
development  of  a climax  deciduous  forest  on  fixed  dunes,  as  found 
in  the  Point  Betsie  region  and  at  other  points  along  the  Michigan 
shore,  is  an  interesting  problem,  the  solution  of  which  should 
materially  be  aided  by  the  evidence  to  be  obtained  from  a study 
of  this  relatively  untouched  region.  As  suggested  by  the  preceding 
morphological  study,  the  climax  forest  which  developed  on  the 
morainic  upland  has  begun  to  invade  the  sand  ridge  area  along  all 
lines  of  contact  between  the  moraines  and  the  sand,  the  under- 
growth having  gone  farthest,  and  the  tree  species  migrating  more 
slowly.  The  first  tree  of  the  climax  forest  to  appear  in  the  sand 
ridges  is  Tsuga  canadensis,  scattered  specimens  of  which  are  found 
up  to  a quarter  or  half  a mile  from  the  morainic  border  in  the  tension 
zone  on  the  west,  and  for  varying  distances  on  the  other  borders  of 
the  sand  ridge  area.  Many  parts  of  the  lowland  border  on  the 
south  have  been  cleared  of  trees,  but  in  the  small  triangle  between 
Long  and  Rush  Lakes  the  deciduous  forest  is  in  contact  with  a 
cedar  swamp,  and  we  can  find  there  a horizontal  succession  in 
practically  untouched  condition.  The  first  hardwood  pioneers  in 
the  swamp  are  Fraxinus  americana,  F.  nigra,  JJlmus  americana, 
, Tilia  americana,  and  Acer  rubrum.  As  Thuja  disappears,  the  trees 
of  the  beech-maple-hemlock  forest  begin  to  come  in  on  an  alluvial 
substratum,  forming  a lake  plain  washed  down  from  the  Algonquin 


IQ 2 2]  WATERMAN— PLANT  COMMUNITIES  2 1 

terrace  on  the  south.  The  largest  trees  have  been  cut,  but  hemlock 
stumps  up  to  four  feet  in  diameter  are  still  to  be  seen. 

On  the  strip  of  land  between  Long  and  Platte  Lakes  a scattered 
and  somewhat  stunted  growth  of  Tsuga  canadensis,  Acer  saccharum, 
and  Fagus  americana  extends  north  almost  to  Michigan  Highway 
22,  over  soil  which  at  first  is  somewhat  alluvial,  but  which 
gradually  changes  into  the  usual  sand  ridge  type.  Toward  the 
north  the  hard  maples  disappear  first  and  the  hemlocks  last,  as 
the  oaks  and  pines  become  more  frequent.  On  the  east  very  little 
uniform  advancement  of  the  deciduous  trees  was  found,  probably 
because  of  the  steep  xerophytic  bluff  occupied  by  conifers  (fig.  7). 
The  valley  of  Otter  Creek  has  not  been  studied  in  detail  as  yet,  but 
it  seems  to  be  largely  occupied  by  conifers,  although  the  soil  condi- 
tions are  more  those  of  an  alluvial  floodplain  than  in  any  other 
part  of  the  sand  ridge  region. 

Apart  from  this  rather  uniform  invasion  along  the  borders, 
there  are  several  isolated  spots  where  hemlocks  at  least  are  found  in 
some  frequency  and  of  considerable  size.  On  the  morainic  ridge 
between  Platte  and  Little  Platte  Lakes  the  deciduous  forest  was 
apparently  well  developed,  with,  however,  a large  proportion  of 
pines  and  some  oaks.  Large  hemlocks  are  found  in  several  places 
along  the  east  bank  of  Platte  River  north  of  Platte  Lake  (fig.  8),  and 
in  the  valley  on  the  south  slope  of  the  morainic  fragment  on  the  shore 
of  Lake  Michigan  (fig.  10).  In  the  last  locality  they  are  in  poor  con- 
dition, and  some  have  recently  died.  Small  specimens  are  to  be  found 
on  the  edges  of  many  of  the  smaller  swamp  depressions,  especially 
on  the  southwest  of  Loon  Lake,  that  is,  on  the  opposite  side  of 
Platte  River  from  the  morainic  ridge  extension  just  mentioned. 
Fagus  americana  has  not  been  found  away  from  the  borders  and 
the  wedge-shaped  invasion  between  Platte  and  Little  Platte  Lakes. 
A solitary  specimen  apparently  about  fifty  years  of  age  is  growing 
by  Michigan  Highway  22,  about  a quarter  of  a mile  west  of 
Platte  River,  and  therefore  in  the  heart  of  the  sand  ridge  area.  Its 
shape  shows  that  it  grew  in  the  open,  but  its  age  does  not  preclude 
the  possibility  of  its  having  been  planted  by  the  first  settlers.  The 
mixed  coniferous-deciduous  lake  bluff  border  association  described 


22 


BOTANICAL  GAZETTE 


[SEPTEMBER 


in  the  Crystal  Lake  Bar  region  (lo)  does  not  appear  in  this  region, 
probably  because  the  corresponding  habitat  is  not  present.  This 
association  contained  Thuja  occidentalism  Abies  halsamea,  Tilia 
americana.  and  Os  try  a virginiana,  mixed  with  the  trees  of  the  chmax 
deciduous  forest  on  the  crest  of  the  bluffs  facing  Lake  Michigan.  It 
was  apparently  due  to  the  exposure  to  sun  and  lake  winds,  combined 
with  low  soil  moisture  content.  The  only  place  where  it  might 
have  been  expected  was  on  the  high  bank  at  the  eastern  edge  of  the 


Fig.  io. — Morainic  remnant  on  shore  of  Lake  Michigan;  landward  slope  equally 
steep,  with  hemlocks  growing  in  valley. 


sand  ridge  region,  and  there  the  only  conifers  seem  to  have  been 
Finns  Strobus  and  P.  resinosa. 

The  preceding  discussion  indicates  that  the  migration  of  the 
beech-maple-hemlock  forest  into  the  sand  ridge  formation  has  been 
of  two  sorts,  one  a general  advance  along  all  Hnes  of  contact 
between  the  two  formations,  the  other  in  a long  slender  belt  on 
the  morainic  ridge  and  its  remains,  to  the  shore  of  Lake  Michigan 
(fig.  lo).  Unpublished  investigations  by  the  writer  indicate  that  for 
the  establishment  of  Thuja  occidentalis  and  Abies  balsamea  on  sandy 
soil  it  is  necessary  that  there  should  be  present  in  the  sand  enough 
moisture  to  carry  the  young  tree  root  below  the  drought  zone.  This 


1922] 


WA  TERM  A N—PLA  NT  COMM  UNITIES 


23 


may  be  held  by  humus  in  the  soil,  or  by  a high  moisture  content  in 
sand  relatively  free  from  humus,  and  it  seeems  possible  that  this 
may  also  be  true  for  Tsuga,  but  not  for  Fagus.  Acer  saccharum 
seemed  to  hold  an  intermediate  position  between  the  two,  and  its 
apparent  absence  from  any  advanced  positions  on  the  sand  ridge 
habitat  was  a distinct  surprise.  Morainic  soil  equally  with  humus 
seems  to  afford  a suitable  substratum  for  the  establishment  of  all 
the  species  mentioned,  either  because  of  the  supply  of  necessary 
mineral  elements,  or  because  these  minerals  make  possible  a better 
utilization  of  the  water  present.  For  these  reasons  the  advance- 
ment of  the  deciduous  formation  seems  to  be  the  result  of  increased 
humus  content  and  mesophytism,  and  also  a pushing  forward  by 
sheer  force  of  numbers.  The  parent  seed  trees  being  so  near  at 
hand  and  supplying  so  many  seeds,  it  follows  that  in  time  a fair 
number  of  seedlings  have  been  able  to  find  conditions  favorable  to 
growth  and  so  become  established.  In  the  other  case,  the  morainic 
substratum  affords  a soil  peculiarly  favorable  to  the  deciduous  trees, 
and  while  a much  smaller  number  of  seeds  have  lodged  on  it,  a 
relatively  larger  proportion  have  become  established.  In  view  of 
the  fact  that  the  shade  and  moisture  conditions  vary  greatly 
on  different  parts  of  this  ridge,  it  would  seem  to  be  the  chemical 
constituents  of  the  soil  which  give  to  it  its  favorable  character- 
istics. 

(The  question  may  be  raised  as  to  whether  this  condition  may 
not  be  the  result  of  the  prehistoric  fires,  previous  to  which  the 
beech-maple-hemlock  elements  may  have  been  more  widely  dis- 
tributed, and  the  present  isolated  groups  may  be  relics  preserved 
because  of  the  protection  of  bodies  of  water)  Against  this  view  may 
be  set  the  evidence  of  tradition  and  the  entire  absence  of  stumps  in 
other  moist  habitats  of  the  region  which  seem  to  have  been  un- 
touched by  fires.  Unquestionably  even  hemlock  stumps  and  logs 
do  not  last  as  long  as  pine,  but  it  might  be  expected  that  some  traces 
would  remain  if  they  had  been  at  all  widespread  in  comparatively 
recent  times.  This,  however,  would  not  account  for  the  appearance 
of  hemlocks  on  the  edges  of  swamps  at  some  distance  from  these 
rehc  patches.  It  is  also  reasonable  to  suppose  that  reforestation 
after  a fire  would  proceed  along  general  lines  similar  to  those  of 


24 


BOTANICAL  GAZETTE 


[SEPTEMBER 


the  original  advance,  so  that  in  either  event  the  stages  of  the  prisere 
would  be  approximately  as  outlined. 

Aquatic  succession  (hydrosere) 

The  substratum  in  this  succession  is  standing  water,  either  in 
closed  depressions  such  as  ponds  and  small  lakes,  or  in. open  depres- 
sions as  bays  or  lagoons  along  the  banks  of  lakes  or  of  Platte  River. 
These  various  bodies  of  water  show  practically  the  same  vegetation 
for  the  first  three  stages,  commonly  designated  as  the  Pota- 
mogeton,  Nymphaea,  and  Scirpus  stages.  After  that  different  lines 
of  succession  are  found,  depending  on  the  condition  of  the  habitat. 

Sand  ridge  depressions  containing  standing  water. — In 
these  depressions  the  water  is  fairly  shallow,  but  the  depression  is 
surrounded  by  sand  ridges  whose  slopes  rise  directly  from  the 
water’s  edge.  Here  are  to  be  found  either  swamp  or  bog  stages 
according  to  the  condition  of  the  substratum.  In  the  swamp  type 
the  fourth  stage  is  a narrow  sedge  zone,  the  shrub  growth  is  scanty, 
mostly  willows,  and  the  sand  ridge  vegetation  descends  the  slopes 
almost  to  the  water’s  edge.  In  the  bog  type  the  quaking  mat  is 
seldom  found,  but  there  is  a dense  growth  of  sedges  and  grasses  on  a 
fairly  solid  muck  foundation.  This  contains  such  bog  plants  as 
Menyanthes  trifoliata,  Potentilla  palustris,  and  occasionally  Sar- 
racenia  purpurea,  and  Sphagnum  sp.  The  shrub  zone  is  a dense 
thicket  of  Alnus  incana,  Pyrus  arhutijolia,  with  some  Hamamelis 
virginiana,  and  sometimes  with  scattered  specimens  of  Thuja 
occidentalis  and  even  Tsuga  canadensis  mingling  with  poplars  and 
the  first  trees  of  the  pine-oak  association.  The  water  is  frequently 
shallow  on  the  north  side  of  the  pond,  possibly  from  sand  blown  in 
by  the  winds  from  Lake  Michigan,  and  of  course  is  exposed  to  the 
heat  of  the  sun,  but  protected  from  the  colder  winds.  The  south 
side  has  deeper  water,  and  is  more  sheltered  from  the  heat  of  the 
sun  on  account  of  the  shade  of  the  pines  and  oaks,  but  exposed 
to  the  cold  winds.  In  depressions  of  this  kind  the  swamp  vegetation 
is  found  on  the  shallow,  warmer,  northern  side,  while  the  bog  type 
occurs  on  the  deeper,  cooler,  southern  side.  In  depressions  which 
are  sheltered  on  all  sides  and  in  which  the  water  is  deep  all  over,  the 
bog  type  generally  prevails  over  the  whole  pond. 


I {>2  2 


[V/1  TERM  A N—PLA  NT  COMMUNITIES 


25 


(in ASS  MKADOW  TYPK. — Hcrc  thc  fourth  stage  is  one  dominated 
by  grasses  and  sedges  forming  a relatively  solid  turf.  In  the  small- 
est depressions  the  sedge  society  may  be  only  a few  yards  square, 
and  in  it  there  are  often  found  swamp  j)lants  such  as  Hypericum 
virginicum,  Spiraea  salicifolia,  and  Rosa  Carolina,  as  well  as  occa- 
sional relics  of  the  acpiatic  stages.  The  later  stages  resemble  those 
of  the  swam])  ty])e  already  described.  The  larger  grass  meadows 
are  relatively  limited  in  number,  only  four  or  five  having  been  dis- 
covered so  far,  and  they  have  certain  peculiar  features  which  seem 
to  demand  s])ecial  consideration.  The  first  is  the  mature  condition 
of  the  extensive  grass  turf,  and  the  other  is  the  absence  of  any 
tendency  of  the  shrubs  and  trees  to  invade  the  meadow.  Where 
the  grass  meadow  is  surrounded  by  a shrub  zone  of  the  swamp  type, 
this  may  be  accounted  for  on  the  assumption  that  the  depression 
was  originally  all  very  shallow,  thus  favoring  a development  of  turf 
so  rapid  that  the  shrubs  and  trees  had  no  chance  to  become  estab- 
lished before  the  mat  of  grass  roots  had  completely  occupied  the 
substratum.  'There  are,  however,  some  features  which  indicate 
that  the  grass  mat  was  formed  recently  and  very  rapidly,  indicating 
j)erha])s  a ])hysiogra])hic  change  in  comparatively  recent  times. 
'These  are  best  shown  in  a grass  meadow  visited  only  once,  as  it  was 
discovered  in  a hurried  reconnoissailce  trip,  and  so  far  there  has 
been  no  oi)i)ortunity  for  a second  visit,  'lliis  meadow  is  located 
just  west  of  the  lower  reaches  of  the  Platte  River  very  near  the 
strij)  of  moving  dunes  on  the  shore.  It  extends  from  northeast  to 
southwest  ])ractically  ii\a  straight  line  for  rather  more  than  half  a 
mile,  but  is  less  than  a hundred  yards  wide  at  the  point  crossed, 
although  somewhat  wider  to  the  east  and  the  west.  At  this  point 
there  were  imbedded  in  the  grass  on  both  edges  of  the  meadow 
trunks  of  dead  trees  extending  out  from  both  banks,  and  on  each 
tree  was  growing  a row  of  tamaracks  apjiarently  not  over  twenty- 
live  years  old.  'There  were  scattered  tamarack  trees  on  the  lower 
edges  of  the  sand  ridges.  While  the  localization  of  the  tamaracks 
on  the  dead  logs  and  not  in  the  grass  is  not  surprising,  the  preserva- 
tion of  the  logs  long  enough  for  the  grass  turf  to  form  and  the 
apparent  youth  of  the  trees  makes  a very  interesting  problem. 
This  meatlow  a])])arently  has  never  been  mowed  or  burned.  The 


26 


BOTANICAL  GAZETTE 


[SEPTEMBER 


logs  may  have  come  from  trees  killed  by  prehistoric  fires,  as  they 
had  no  bark  on  them,  but  they  were  not  charred,  and  otherwise 
seemed  well  preserved,  with  many  dead  branches  extending  up 
among  the  young  tamarack  trees.  In  fact,  the  whole  situation 
suggested  the  sudden  freezing  of  the  surface  of  a pond,  solidifying 
into  a green  grass  mat,  instead  of  a covering  of  ice.  In  the  case  of 
the  large  meadow  occupying  a shallow  swale  between  Long  and 
Rush  Lakes,  which  at  one  time  might  have  been  a water  connection 
between  the  two  lakes,  the  shore  showed  the  regular  horizontal 


Fig.  II. — Grass  meadow  near  Long  Lake;  bog  shrubs  on  left,  with  tamaracks  and 
cedar  swamp  behind  them. 


stages  of  a bog-cedar  forest  succession,  but  the  center  of  the  swale 
is  occupied  by  a meadow  with  solid  turf  (fig.  ii).  The  meadow 
has  been  mowed  for  years,  and  was  recently  ditched  for  draining, 
but  this  treatment  apparently  has  not  changed  the  general 
relations.  The  shrub  zone  at  its  southern  edge  is  the  usual  bog 
shrub  stage,  followed  by  a belt  of  tamaracks  of  considerable  size. 
A mature  cedar  forest  adjoins  this  on  the  south,  with  a fairly  dry 
substratum  and  some  of  the  undergrowth  elements  of  the  deciduous 
forest.  Next  come  deciduous  swamp  trees,  and  finally  the  trees  of 
the  climax  forest.  Here  we  have  a bog  forest  left  high  and  relatively 
dry,  with  a grass  meadow  formed  at  its  edge. 


922] 


WATERMAN— PLANT  COMMUNITIES 


27 


Each  of  these  formations,  although  differently  situated  (one 
in  the  heart  of  the  sand  ridges,  the  other  between  two  lakes) , seems 
to  indicate  the  same  physiographic  change,  that  is,  a sudden  lower- 
ing of  the  water  table  by  several  feet.  This  change  might  be 
referred  to  the  activities  of  the  first  white  settlers  about  fifty  years 
ago.  The  Long  Lake  area  is  very  close  to  Crystal  Lake,  and  might 
have  been  partially  drained  by  seepage  when  Crystal  Lake  level 
was  lowered  101871(10).  A low  terrace  on  the  south  bank  of  Long 
Lake  adds  weight  to  this  hypothesis.  The  other  meadow  must 
have  come  very  close  to  Platte  River  at  its  eastern  extremity,  and 
may  have  been  lowered  in  connection  with  the  first  lumbering  opera- 
tions at  about  the  same  time. 

Another  explanation  of  the  lowering  of  the  water  is  based  on 
diastrophic  changes.  Observations  on  the  shore  of  Lake  Michigan, 
both  on  the  Michigan  side  and  on  the  Green  Bay  Peninsula  opposite, 
indicate  that  fifty  years  ago  the  lake  was  several  feet  higher  than 
the  highest  levels  of  recent  years,  and  this  fall  of  level  might  have 
affected  the  level  of  Platte  River  in  its  lower  reaches  (fig.  12). 
There  are  also  extensive  meadows  bordering  Platte  River  and  the 
sluggish  stream  connecting  Platte  and  Little  Platte  Lakes,  whose 
origin  may  be  connected  with  the  lowering  of  water  levels  at 
about  the  same  time.  Further  study,  both  of  the  floristic  content 
and  of  the  nature  of  the  substratum,  is  necessary  before  defiinite 
conclusions  can  be  reached.  There  is  no  indication  of  any  migra- 
tion of  trees  into  a grass  meadow  with  solid  grass  mat,  whether 
large  or  small,  but  there  seems  to  be  some  evidence  that  they  can 
come  in  on  a floating  mat  of  the  swamp  type.  Further  investigation 
may  show  that  the  latter  case  is  really  a bog  mat,  in  which  event 
it  would  not  be  available  as  evidence,  and  the  presence  of  trees 
would  be  quite  in  accordance  with  the  rule  for  bog  mats. 

Bog  type. — Here  the  fourth  stage  develops  as  a bog  mat  com- 
posed of  sphagnum  and  the  usual  accompanying  bog  plants.  In 
several  cases  this  has  developed  into  an  ericad  heath  composed 
largely  of  Chamaedaphne,  Andromeda,  occasionally  Ledum  and 
similar  shrubs,  including  Betula  pumila,  and  scattered  trees  of 
Larix,  Picea  mariana,  and  occasionally  Pinus  Strobus  and  P.  resi- 
nosa.  In  other  cases  the  tamaracks  with  some  bog  shrubs  and 


28 


BOTANICAL  GAZETTE 


[SEPTEMBER 


Thuja  have  come  in  very  thickly,  forming  a bog  thicket  which  in 
some  cases  apparently  may  develop  into  a cedar  forest.  The 
tamaracks  in  this  region  are  all  small,  with  the  exception  of  those 
between  the  shrub  belt  and  the  cedar  forest  already  noted  between 
Long  and  Platte  Lakes.  The  occurrence  of  bog  vegetation  in  the 
depressions  among  sand  ridges  has  already  been  noted.  The  varia- 
tion in  depth  on  opposite  sides  also  applies  to  some  extent  to  the 
larger  ponds  and  lakes.  In  the  latter  cases  the  shallow  portions 
are  characterized  by  extensive  Scirpus  colonies,  but  the  bog  asso- 


Fig.  12. — Lower  reaches  of  Platte  River,  bordered  by  grass  meadows,  with  some 
second  growth  birches;  sand  ridges  in  distance. 


ciations  do  not  appear  along  the  shores  of  the  lakes.  In  open 
bays  and  lagoons  there  was  no  general  uniformity,  but  swamp 
or  bog  types  were  found  corresponding  to  the  varying  local  condi- 
tions. From  this  it  is  concluded  that  the  development  of  the  later 
stages  of  the  hydrosere  into  the  swamp  or  the  bog  type  is  dependent 
chiefly  on  depth  of  water  and  temperature.  Investigations  as  to 
acidity  have  not  been  made  as  yet,  but  it  is  assumed  that  here,  as 
elsewhere,  the  swamp  type  will  be  associated  with  a neutral  or 
alkaline  condition  and  the  bog  type  with  high  acidity.  The  tree 
stage  in  the  hydrosere  was  found  to  follow  only  the  quaking  mat 


1922] 


WA  TERM  A N— PLANT  COMM  UNITIES 


29 


stage,  and  not  the  grass  meadow.  If  we  accept  the  hypothesis  for 
the  very  recent  formation  of  the  large  grass  meadows,  the  absence 
of  trees  might  be  attributed  to  shortness  of  time,  but  the  same 
condition  is  found  in  the  smallest  meadows,  which  from  their  posi- 
tion and  general  appearance  must  be  regarded  as  contemporaneous 
with  the  wet  depressions  and  with  the  sand  ridges  themselves,  and 
here  there  should  have  been  ample  time  for  invasion.  It  does  not 
follow  necessarily  that  the  grass  meadow  is  an  edaphic  climax,  but 
it  is  evident  that  that  association  will  remain  stable  for  a very  long 
time.  As  already  noted,  the  bog  mat  passes  relatively  rapidly  into 
a tamarack  cedar  forest,  which  quickly  receives  hydrophytic  decidu- 
ous elements,  and  thus  passes  into  the  climax  deciduous  forest. 

Summary 

1.  Genetic  synecology  is  that  part  of  ecology  which  deals  with 
the  developmental  relations  of  plant  communities.  In  a limited 
region  the  development  of  successions  (seres)  is  definitely  related 
to  the  character  of  the  substratum.  In  this  region  two  such  seres 
are  found,  the  sand  succession  (psammosere)  and  the  aquatic 
succession  (hydrosere).  The  clay-gravel  succession  (geosere)  has 
reached  its  climax  on  the  surrounding  moraines,  and  is  observed 
only  as  it  invades  the  sand  ridge  region. 

2.  In  this  study  the  successional  units,  the  concrete  association 
and  formation,  are  defined  as  follows.  The  association  is  a plant 
community  of  essentially  uniform  (or  homogeneous)  physiognomy 
and  ecological  structure,  and  of  essentially  uniform  (or  homo- 
geneous) floristic  composition  as  regards  dominant  species.  The 
formation  is  an  association-complex  characterized  by  a dominant 
association,  but  including  all  adjacent  associations,  whether  mature 
or  immature,  and  other  more  or  less  anomalous  or  unidentified  com- 
munities associated  with  them.  The  unit  above  the  formation  is  a 
formation  complex,  or  aggregate,  and  is  composed  of  the  formations 
of  a definite  region  which  may  be  limited  by  climatic  or  geographic 
boundaries.  The  ground  occupied  by  an  association  is  called  a 
locahty,  that  occupied  by  a formation  an  area,  and  that  occupied  by 
a formation  complex  a region. 

3.  The  vegetation  of  the  region  studied  is  found  to  be  a forma- 
tion complex  consisting  of  a sand  dune  formation,  a sand  ridge 


30 


BOTANICAL  GAZETTE 


[SEPTEMBER 


formation,  and  swamp  and  bog  formations.  It  occupies  a region 
which  consists  of  sand  ridges  with  depressions  containing  bodies 
of  water  of  all  sizes,  from  a few  yards  to  a mile  or  more  in  diameter. 
Geologically  the  region  was  a shallow  bay  of  Lake  Algonquin 
drained  by  the  recession  of  the  waters  of  the  lake  with  the  melting 
of  the  ice  barrier  in  the  Straits  of  Mackinaw. 

4.  The  first  stages  of  the  sand  succession  (psammosere)  are 
found  in  the  moving  dune  belt  along  the  shore,  but  they  do  not 
lead  to  a complete  stabilization  of  the  sand.  The  later  stages 
appear  when  the  sand  stops  moving  as  a result  of  a checking  of  the 
force  of  the  wind,  due  to  distance  from  the  shore  or  the  formation 
of  high  dunes  which  act  as  windbreaks.  The  pine-oak  stage  shows 
a progressive  change  from  the  less  mature  areas  near  the  lake  to 
the  more  mesophytic  areas  in  the  southern  portion  of  the  region. 
Soil  moisture  content  and  the  amount  of  humus  in  the  sand  seem 
to  be  important  factors  in  this  change. 

5.  The  clay-gravel  succession  (geosere)  has  reached  the  climax 
stage  as  a beech-maple-hemlock  forest  on  the  surrounding  morainic 
upland,  and  is  found  invading  the  pine-oak  formation  along  the 
borders  of  the  region,  and  especially  along  a narrow  morainic  tongue 
which  extends  completely  through  the  sand  ridge  substratum  to 
Lake  Michigan.  The  controlling  factor  in  this  invasion  seems  to  be 
primarily  the  chemical  character  of  the  soil,  glacial  material  ranking 
close  to  humus  in  importance,  and  secondarily  the  soil  moisture 
content. 

6.  The  various  ponds  and  lakes  all  show  the  normal  early  stages 
of  the  aquatic  succession  (hydrosere),  which  lead  either  to  swamp 
meadows  or  to  bog  forests,  the  line  of  development  followed  being 
determined  chiefly  by  depth  of  water  and  exposure  to  the  heat  of 
the  sun. 

Northwestern  University 
Evanston,  III. 


LITERATURE  CITED 

1.  Clements,  F.  E.,  Plant  succession.  Carnegie  Publ.  no.  242.  1916. 

2.  Cooper,  W.  S.,  The  climax  forest  of  Isle  Royale,  Lake  Superior,  and  its 
development.  Box.  Gaz.  55: 1-44.  1913. 


WA  TERM  A N— PLANT  COMM  UNITIES 


31 


1922] 

3.  Cowles,  H.  C.,  The  physiographic  ecology  of  Chicago  and  vicinity,  a 
study  of  the  origin,  development,  and  classification  of  plant  societies. 
Box.  Gaz.  31:73-108;  145-182.  1901. 

4.  , The  causes  of  vegetative  cycles.  Box.  Gaz.  51:161-183.  1911. 

5.  Moss,  C.  E.,  Geographical  distribution  of  vegetation  in  Somerset.  Royal 
Geog.  Soc.  1907. 

6.  Nichols,  G.  E.,  The  interpretation  and  application  of  certain  terms  and 
concepts  in  the  ecological  classification  of  plant  communities.  Plant 
World  20:305-319;  341-353*  1917* 

7.  , Abstract  in  printed  program  of  Ecolog  il  Society  of  America  for 

Meeting  at  Toronto,  December,  1921. 

8.  Tansley,  a.  G.,  Types  of  British  vegetation.  ambridge.  1911. 

9.  , The  classification  of  vegetation  and  the  concept  of  development. 

Jour.  Ecology  8:118-149.  1920. 

10.  Waxerman,  W.  G.,  Ecology  of  Crystal  Lake  Bar  region.  Ann.  Report 
Mich.  Acad.  Sci.  19:197-208.  1917. 

11.  — , Development  of  root  systems  under  dune  conditions.  Box.  Gaz. 

68:22-53.  1919. 

12.  Whixford,  H.  N.,  The  genetic  development  of  the  forests  of  Northern 
Michigan.  Box.  Gaz.  31: 289-325.  1901. 


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Syracuse,  N.  Y. 
Stockton,  Calif. 


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